From e1600104410cb7e842cc7cbb9fa47047c60ad40f Mon Sep 17 00:00:00 2001
From: Stefan Harmuth <stefan.harmuth@docomodigital.com>
Date: Sun, 24 Oct 2021 13:55:06 +0200
Subject: [PATCH] new idea for d19p2 actually works 2015 finished!

---
 day19/day.go | 96 +++++++++++++++++++++++++---------------------------
 1 file changed, 46 insertions(+), 50 deletions(-)

diff --git a/day19/day.go b/day19/day.go
index 15d9700..7aeed31 100644
--- a/day19/day.go
+++ b/day19/day.go
@@ -1,6 +1,8 @@
 package day19
 
 import (
+	"fmt"
+	"os"
 	"strings"
 	"tools"
 )
@@ -42,63 +44,57 @@ func Part1(puzzle tools.AoCPuzzle) interface{} {
 	return len(outcomes)
 }
 
-func getPossibleTransformations(from tools.Set, replacments map[string]tools.Set, maxLen int) tools.Set {
-	returnSet := tools.NewSet()
-	var result string
-
-	for interfaceMolecule := range from {
-		currentMolecule := interfaceMolecule.(string)
-		for i := range currentMolecule {
-			if transSet, ok := replacments[string(currentMolecule[i])]; ok {
-				for replacement := range transSet {
-					result = currentMolecule[:i] + replacement.(string)
-					if i < len(currentMolecule)-1 {
-						result += currentMolecule[i+1:]
-					}
-					if len(result) <= maxLen {
-						returnSet.Add(result)
-					}
-				}
-			}
-			if i < len(currentMolecule)-1 {
-				if transSet, ok := replacments[currentMolecule[i:i+2]]; ok {
-					for replacment := range transSet {
-						result = currentMolecule[:i] + replacment.(string)
-						if i < len(currentMolecule)-2 {
-							result += currentMolecule[i+2:]
-						}
-						if len(result) <= maxLen {
-							returnSet.Add(result)
-						}
-					}
-				}
-			}
-		}
-	}
-
-	return returnSet
-}
-
 func Part2(puzzle tools.AoCPuzzle) interface{} {
 	input := puzzle.GetInputArray()
 	molecule := input[len(input)-1]
 	replacementStrings := input[:len(input)-2]
-	replacements := make(map[string]tools.Set)
-	for _, line := range replacementStrings {
-		parts := strings.Split(line, " => ")
-		if _, ok := replacements[parts[0]]; !ok {
-			replacements[parts[0]] = tools.NewSet()
+
+	replacements := make(map[string]string)
+	replacementLengths := make(map[int][]string)
+	var maxLen, minLen int
+	for _, s := range replacementStrings {
+		parts := strings.Split(s, " => ")
+		if _, ok := replacements[parts[1]]; ok {
+			fmt.Println("Double target string found!")
+			os.Exit(1)
+		} else {
+			replacements[parts[1]] = parts[0]
+			x := len(parts[1])
+			if x > maxLen {
+				maxLen = x
+			}
+			if x < minLen {
+				minLen = x
+			}
+			if _, ok := replacementLengths[x]; ok {
+				replacementLengths[x] = append(replacementLengths[x], parts[1])
+			} else {
+				replacementLengths[x] = []string{parts[1]}
+			}
 		}
-		replacements[parts[0]].Add(parts[1])
 	}
 
-	currentMolecules := tools.NewSet()
-	currentMolecules.Add("e")
-	transformCount := 0
-	for !currentMolecules.Contains(molecule) {
-		transformCount++
-		currentMolecules = getPossibleTransformations(currentMolecules, replacements, len(molecule))
+	steps := 0
+	foundSomething := false
+	for len(molecule) > 1 {
+		foundSomething = false
+		for x := maxLen; x >= minLen; x-- {
+			for _, replacement := range replacementLengths[x] {
+				if strings.Contains(molecule, replacement) {
+					molecule = strings.Replace(molecule, replacement, replacements[replacement], 1)
+					foundSomething = true
+					steps++
+					break
+				}
+			}
+			if foundSomething {
+				break
+			}
+		}
+		if !foundSomething {
+			break
+		}
 	}
 
-	return transformCount
+	return steps
 }